The Windiest Planet Dark, cold and whipped by supersonic winds, Neptune is the last of the hydrogen and helium gas giants in our solar system. More than 30 times as far from the sun as Earth, the planet takes almost 165 Earth years to orbit our sun. In 2011 Neptune completed its first orbit since its discovery in 1846.

In the case of a comet, the tail is a long link of gas and dust that flow away from the nucleus and coma of the comet.

tectonic

Deformation forces acting on a planet's crust.

tectonism

The processes of faulting, folding or other deformation of the lithosphere of a planetary body, often the result of large-scale internal movements below the lithosphere.

terminator

The dividing line between the illuminated and the unilluminated part of the moon's or a planet's disk. The line of sunrise or sunset on a planet or its satellite. At dawn and dusk when the sun is lowest in the sky (low sun), topographic features cast their longest shadows. This reveals information about the size and shape of the objects casting the shadows. Therefore, features near the terminator are imaged in order to obtain morphologic information.

terra

An extensive land mass.

terrain

The surface features of an area of land.

terrestrial planets

The inner solar system planets: Mercury, Venus, Earth, Mars, composed of rocky materials and iron, with a density between 4.0 and 5.5 grams per cubic centimeter.

tessera

Tile; terrain formed of polygonal pattern

texture

The general appearance or character of a rock. (e.g. the size, shape, and arrangement of its constituent elements)

tholus

small domical mountain or hill.

tidal heating

Frictional heating of a satellite's interior due to flexure caused by the gravitational pull of its parent planet and possibly neighboring satellites.

topography

The general configuration of a land surface.

torus

A shape that resembles a doughnut or the inner-tube of a tire.

trailing hemisphere

The hemisphere that faces backwards, away from the direction of motion of a satellite that keeps the same face toward the planet.

Trojan

An object orbiting in the Lagrange points of another (larger) object. This name derives from a generalization of the names of some of the largest asteroids in Jupiter's Lagrange points: 588 Achilles, 624 Hektor, and 911 Agamemnon. Saturn's satellites Helene, Calypso and Telesto are also sometimes called Trojans.

troposphere

The layer of the atmosphere from the surface to where the temperature stops decreasing with height.

In the case of a comet, the tail is a long link of gas and dust that flow away from the nucleus and coma of the comet.

tectonic

Deformation forces acting on a planet's crust.

tectonism

The processes of faulting, folding or other deformation of the lithosphere of a planetary body, often the result of large-scale internal movements below the lithosphere.

terminator

The dividing line between the illuminated and the unilluminated part of the moon's or a planet's disk. The line of sunrise or sunset on a planet or its satellite. At dawn and dusk when the sun is lowest in the sky (low sun), topographic features cast their longest shadows. This reveals information about the size and shape of the objects casting the shadows. Therefore, features near the terminator are imaged in order to obtain morphologic information.

terra

An extensive land mass.

terrain

The surface features of an area of land.

terrestrial planets

The inner solar system planets: Mercury, Venus, Earth, Mars, composed of rocky materials and iron, with a density between 4.0 and 5.5 grams per cubic centimeter.

tessera

Tile; terrain formed of polygonal pattern

texture

The general appearance or character of a rock. (e.g. the size, shape, and arrangement of its constituent elements)

tholus

small domical mountain or hill.

tidal heating

Frictional heating of a satellite's interior due to flexure caused by the gravitational pull of its parent planet and possibly neighboring satellites.

topography

The general configuration of a land surface.

torus

A shape that resembles a doughnut or the inner-tube of a tire.

trailing hemisphere

The hemisphere that faces backwards, away from the direction of motion of a satellite that keeps the same face toward the planet.

Trojan

An object orbiting in the Lagrange points of another (larger) object. This name derives from a generalization of the names of some of the largest asteroids in Jupiter's Lagrange points: 588 Achilles, 624 Hektor, and 911 Agamemnon. Saturn's satellites Helene, Calypso and Telesto are also sometimes called Trojans.

troposphere

The layer of the atmosphere from the surface to where the temperature stops decreasing with height.